The present invention relates to a method for the preparation of a novel polyoxyalkylene polyether modified at the chain terminals thereof with organosilicon-containing groups and a room temperature-curable composition formulated with the polyoxyalkylene polyether.
In the prior art, there are known a wide variety of so-called room temperature-curable compositions stable and storable when kept with hermetic sealing but capable of rapidly being cured when exposed to the atmospheric air containing moisture even at room temperature to be converted into a rubbery solid. These compositions are classified into so-called "two-package" and "one-package" types. The compositions of the former type are prepared and stored in two packages containing different kinds or different combinations of the components and the contents of the two packages are blended directly before use of the composition while the compositions of the latter type are prepared by blending all of the components and storable as such with stability in one package. The one package type compositions are preferred, of course, owing to the convenience and better workability, especially, when the composition is directed to the use such as a sealing material, adhesive agent and the like.
As a class of such room temperature-curable compositions are known several kinds of organopolysiloxane compositions crosslinkable and curable by the hydrolysis-condensation reaction of hydrolyzable groups bonded to the silicon atoms including acyloxy groups, amino groups, oxime groups, aminoxy groups, alkoxy groups and the like.
These silicone compositions produce various kinds of condensation products according to the types of the condensation reaction such as carboxylic acids, e.g. acetic acid, amines, oximes, alcohols, amides, ketones and the like.
Some of the problems in these organopolysiloxane-based curable compositions are the water-repellency and oil-repellency of the surfaces of the cured products thereof leading to poor adhesion of aqueous or oily paints and, on the contrary, increased sticking of dusts and dirts as well as the expensiveness of the silicone products in general so that their use as a sealing material or adhesive agent is limited.
On the other hand, there are also known and widely used polysulfide-based and polyurethane-based curable compositions. However, the polysulfide-based curable compositions are defective due to the necessity of formulating a peroxide compound such as lead peroxide, calcium peroxide, manganese peroxide and the like as the curing agent bringing about a problem of toxicity and environmental pollution by these peroxide compounds as well as due to their inherently poor anti-weathering resistance and heat stability. The polyurethane-based curable compositions suffer from the problems of foaming in the course of curing, and yellowish coloring and poor water resistance of the cured products.
There has recently been proposed a room temperature-curable composition based on a polyoxyalkylene polyether modified at both chain terminals with organosilyl groups having hydrolyzable atoms or groups bonded to the silicon atoms (see, for example, Japanese Patent Disclosure No. 50-156599). The organosilicon-modified polyoxyalkylene polyether is prepared by the addition reaction of a polyoxyalkylene polyether having allyl groups at both terminals of the chain molecules thereof with a silane compound having a hydrogen atom directly bonded to the silicon atom and at least one hydrolyzable atom or groups bonded to the silicon atom as represented by the general formula. EQU H-Si(R).sub.b (X).sub.3-b',
where R is an monovalent organic group, e.g. hydrocarbon group, X is a hydrolyzable atom or group and b is a number of zero, 1 or 2.
The organosilicon-modified polyoxyalkylene polyether of the above described type has several problems as follows. When the hydrolyzable atom or group denoted by X is a halogen atom, it must be first converted into a hydrolyzable group by reacting with an alcohol, carboxylic acid, amine, acid amide, dialkylhydroxylamine or oxime compound. When the hydrolyzable group denoted by X is an alkoxy group, a considerably large amount of a curing catalyst such as a metal salt of carboxylic acids is required to be formulated in the composition leading necessarily to decreased heat stability and anti-weathering resistance of the cured products.
Furthermore, when the group X is an acyloxy group, a corrosive gas with unpleasant odor is produced in the course of curing such as a carboxylic acid which also limits the formulation of a filler with basicity in the composition. When the group X is an acid amide group, the instability of the silane compound of the above given general formula retards and disturbs quantitative proceeding of the addition reaction between the allyl-terminated polyoxyalkylene polyether and the silane compound.